Add a function for parsing RFC 5280's "Certificate".

net/cert/internal/parse_certificate.h

Index: net/cert/internal/parse_certificate.h
diff --git a/net/cert/internal/parse_certificate.h b/net/cert/internal/parse_certificate.h
new file mode 100644
index 0000000000000000000000000000000000000000..ebf1b1a957b4d75622cdb6a316f178921d5c2bb4
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+++ b/net/cert/internal/parse_certificate.h
@@ -0,0 +1,69 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef NET_CERT_INTERNAL_PARSE_CERTIFICATE_H_
+#define NET_CERT_INTERNAL_PARSE_CERTIFICATE_H_
+
+#include "base/basictypes.h"
+#include "base/compiler_specific.h"
+#include "net/base/net_export.h"
+#include "net/der/input.h"
+#include "net/der/parse_values.h"
+
+namespace net {
+
+struct ParsedCertificate;
+
+// Parses a DER-encoded "Certificate" as specified by RFC 5280. Returns true on
+// success and sets the results in |out|.
+//
+// Note that on success |out| aliases data from the input |certificate_tlv|.
+// Hence the fields of the ParsedCertificate are only valid as long as
+// |certificate_tlv| remains valid.
+//
+// On failure |out| has an undefined state. Some of its fields may have been
+// updated during parsing, whereas others were not changed.
+//
+// Refer to the per-field documention of the ParsedCertificate structure for
+// details on what validity checks parsing performs.
+//
+//       Certificate  ::=  SEQUENCE  {
+//            tbsCertificate       TBSCertificate,
+//            signatureAlgorithm   AlgorithmIdentifier,
+//            signatureValue       BIT STRING  }
+NET_EXPORT bool ParseCertificate(const der::Input& certificate_tlv,
+                                 ParsedCertificate* out) WARN_UNUSED_RESULT;
+
+// ParsedCertificate contains pointers to the main fields of a DER-encoded RFC
+// 5280 "Certificate".
+//
+// ParsedCertificate is expected to be filled by ParseCertificate(), so
+// subsequent field descriptions are in terms of what ParseCertificate() sets.
+struct NET_EXPORT ParsedCertificate {
+  // Corresponds with "tbsCertificate" from RFC 5280:
+  //         tbsCertificate       TBSCertificate,
+  //
+  // This contains the full (unverified) Tag-Length-Value for a SEQUENCE. No
+  // guarantees are made regarding the value of this SEQUENCE.
+  der::Input tbs_certificate_tlv;
+
+  // Corresponds with "signatureAlgorithm" from RFC 5280:
+  //         signatureAlgorithm   AlgorithmIdentifier,
+  //
+  // This contains the full (unverified) Tag-Length-Value for a SEQUENCE. No
+  // guarantees are made regarding the value of this SEQUENCE.
+  //
+  // This can be further parsed using SignatureValue::CreateFromDer().
+  der::Input signature_algorithm_tlv;
+
+  // Corresponds with "signatureValue" from RFC 5280:
+  //         signatureValue       BIT STRING  }
+  //
+  // Parsing guarantees that this is a valid BIT STRING.
+  der::BitString signature_value;
+};
+
+}  // namespace net
+
+#endif  // NET_CERT_INTERNAL_PARSE_CERTIFICATE_H_